The present invention relates to a speed gearbox used, for instance in automobile vehicles and particularly those in which the transmission between the actuating axle and the driven axle increases in a lineal mode and uninterruptedly.
It is an object of this invention to ease handling of the gearbox and to ease mounting for same.
As it is well known, the gearboxes for automobiles and similar objects, have the purpose of establishing at all times the most ideal relationship between the impulsive force of the motor and the sped of advancement of the vehicle, in a way that in "short" speeds and for a certain power of the motor, the torque supplied to the driving wheels is great and the speed of advancement, small, and vice-versa.
As it is also well known, presently, the majority of gearboxes for vehicles have four or five speeds, besides the unavoidable "back motion", the values of which are generally around 1/4 W, 1/2 W, 3/4 W, W and 5/4 W, wherein W the speed of rotation of the driving shaft. These speeds imply, respectively, the existence of torques at the tractor shaft with a 4p, 1p, 4/3p, p and 4/5p value, wherein p is the motor torque.
The change of any speed to the immediate former or latter one, assumes a sudden jump which is dampened due to the use of the classical clutch.
Although this solution is of the mostly generalized use, there are other gearing mechanisms in which there is no "jump" when changing from one speed to the immediate one, which change is produced continually, consequently making the clutch unnecessary.
Within this type of gears, called friction gears, there exists a group which is based on the use of two contrapositioned cones, with the same conical semi-angle and with parallel shafts.
The basic idea of this type of friction gears is known for a very long time and is schematically represented in FIG. 1, where the cited cones are referenced with 1 and 2, and their respective shafts with 3 and 4.
The shaft of one of these cones is coupled to the motor and the other to the differential of the vehicle. The transmission of the movement from one cone to the other is carried out with the cooperation of an intermediate wheel 5, the axle 6 of which is coplanary, regarding shafts 3 and 4 and parallel to each locus of points 7 and 8 at which contact of the wheel 5 is made with said cones 1 and 2. The cones are only capable to rotate on their respective shafts 3 and 4, whilst the wheel 5, besides rotating, is capable to perform axial movements.
The rotation of the actuating cone 1 is transmitted to the tractor 2 due to a great friction arising between the wheel 5 and both cones, as the cones press strongly between the locus of points 7 and 8 at which contact is made. It has to be added that the materials of which the cones and wheels are made, provide a high friction coefficient.
As can be understood from FIG. 1, for a rotation speed W.sub.1 of the actuating cone 1, the corresponding speed of the tractor cone 2 will depend on the position of the wheel 5, and its value will be W.sub.2 =W.sub.1 R.sub.1 /R.sub.2, which value, to change the speed, may be varied by moving at will the wheel 5 along its axle 6, with which will vary the values R.sub.1 and R.sub.2 and therefore, the value W.sub.2, and all of it in a lineal mode.
This solution, apparently ideal, is in practice most inconvenient, because to move axially the wheel 5 it is necessary to apply a great effort to overcome the friction which keeps the cones and the wheel tightly linked. Such a mechanism has hardly been utilized for this reason.